The invention relates to a method for manufacturing a display device having a display window and in front of the display window an auxiliary transparent plate, in which method the display window and the transparent plate are positioned at some distance from each other, the display window and the auxiliary are attached to each other around the edges by a seal, the seal having at least one opening, the volume between the display window and the auxiliary plate being filled with curable material, whereafter the curable material is cured.
Such display devices are known. The display device may comprise for instance a CRT (Cathode Ray Tube) or a PDP (Plasma Display Panel) or an LCD (liquid Crystal Display). The auxiliary plate may be for instance a plate which has an anti-reflective coating or a plate which forms a touch-screen. The auxiliary plate may also be used to enhance the implosion protection. The auxiliary plate is positioned at some distance from the display window (for said purpose spacers may be used). The edges are but for at least one filling opening sealed, thus forming a volume for curable material. Through the opening in the seal curable material is introduced in the volume between the display window and the auxiliary plate. U.S. Pat. No. 5,072,301 describes a method in which display device is so oriented that the display window and the auxiliary plate are oriented vertically, the filling opening being provided at the lowest corner of the gasket formed by the display window, the auxiliary plate and a seal around the edges. Uncured resin is introduced through the filling opening, air being released through an opening at an opposite corner. Near said second opening a sensor is provided for detection of resin. When said sensor detects resin the flow of resin through the filling opening is stopped. The resin is then partially cured, whereafter the flexible seal is removed and the resin is fully cured.
Although the known method does provide for an auxiliary plate to be attached to a display window the position of the auxiliary plate is not well defined and in particular tends to bulge outwards or inwards. Lately more and more emphasis is placed on the amount of flatness of the outer surface of the display device, i.e. the surface at which the viewer is looking. Also the cost of the resin is especially for large size models (more than 20xe2x80x3) appreciable.
It is an object of the invention to provide a method in which the position of the auxiliary plate is better definable and/or the amount of resin used may be reduced.
To this end the method is characterized in that the display window and the auxiliary plate are oriented at an first angle of tilt xcex11 to the horizontal direction, preferably substantially vertically, the volume is partially filed with uncured resin up to a selected level height, the opening being at or near the highest point, thereafter the angle of tilt is reduced to a second angle xcex12 smaller than the first angle xcex11, and when the resin has reached the opening the resin near the opening is cured to plug the opening, whereafter the angle of tilt is reduced to a third angle xcex13, preferably substantially zero, and the rest of the resin is fully cured.
In the known methods the uncured material (here further for simplicity also named xe2x80x98resinxe2x80x99) exerts a force on the auxiliary plate, actually forcing the plate to bulge outwards. This results in an unwanted bulge in the auxiliary plate and furthermore results in more resin being used than is necessary.
In the method in accordance with the invention the volume formed by the display window, the auxiliary plate and the seal is filled with resin. It is not completely filled, but account is taken of the fact that the weight of the resin and the plate forces, in the initial position (i.e. at an angle of tilt xcex11), the auxiliary plate to bulge outwards. As the orientation of the display window is made more horizontally (i.e. reducing the angle of tilt to a second angle xcex12 smaller than xcex11), the weight of the plate and the resin will reduce the bulge, forcing the resin to fill more an more of the volume (actually the volume reduces, while the amount of resin stays the same), until the resin reaches the said opening. This situation is reached at an angle xcex12 which is larger than zero, i.e. still at an angle, be it a relatively small one (for instance 5-25 degrees). In such circumstances the shape of the auxiliary plate tends to better follow the contour of the outer side of the display window and overall the position of the auxiliary plate vis-à-vis the display window shows less deviations from a constant value. Nevertheless there is slightly (for instance 5-15%) more uncured resin in the volume than needed, i.e. the volume is slightly overfilled. The opening is plugged, preferably by locally curing the resin to prevent resin from flowing out of the said volume. Locally curing the resin, has, in contrast to using plugs, a number of advantages. It is fast, there is no chance of resin being spilled outside the display window and there is no or little chance of air being trapped. Thereafter the angle is further reduced to a third angle of tilt xcex13, preferably to zero degrees, i.e. to a horizontal positioning of the display window and the auxiliary plate. The rest of the resin is then cured. Curing will reduce the volume of the resin. The overall thickness of the resin layer is reduced, and better controllable thus resulting in a decreased amount of resin used and a better controllable outside contour. The volume is filled at the angle xcex11 to a selected level. Rather than filing a fixed amount of resin, the volume is filled to a selected level height. This enables to correct for any deviations in the volume.
Preferably the curable material near the opening is cured using an UV light source, while a gas flow of non-reactive gas is provided.